linux-kernel - Re: [PATCH] amdgpu: fix gcc -Wrestrict warning

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Message-ID: <382fd12d804ac8e2693f92cf649c4f038f9c022e.camel@perches.com>
Date:   Wed, 24 Mar 2021 07:31:58 -0700
From:   Joe Perches <joe@...ches.com>
To:     Arnd Bergmann <arnd@...nel.org>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     Arnd Bergmann <arnd@...db.de>, Huang Rui <ray.huang@....com>,
        Jinzhou Su <Jinzhou.Su@....com>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] amdgpu: fix gcc -Wrestrict warning

On Tue, 2021-03-23 at 14:04 +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> gcc warns about an sprintf() that uses the same buffer as source
> and destination, which is undefined behavior in C99:
> 
> drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c: In function 'amdgpu_securedisplay_debugfs_write':
> drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c:141:6: error: 'sprintf' argument 3 overlaps destination object 'i2c_output' [-Werror=restrict]
>   141 |      sprintf(i2c_output, "%s 0x%X", i2c_output,
>       |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   142 |       securedisplay_cmd->securedisplay_out_message.send_roi_crc.i2c_buf[i]);
>       |       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c:97:7: note: destination object referenced by 'restrict'-qualified argument 1 was declared here
>    97 |  char i2c_output[256];
>       |       ^~~~~~~~~~
> 
> Rewrite it to remember the current offset into the buffer instead.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c
> index 834440ab9ff7..69d7f6bff5d4 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c
> @@ -136,9 +136,10 @@ static ssize_t amdgpu_securedisplay_debugfs_write(struct file *f, const char __u
>  		ret = psp_securedisplay_invoke(psp, TA_SECUREDISPLAY_COMMAND__SEND_ROI_CRC);
>  		if (!ret) {
>  			if (securedisplay_cmd->status == TA_SECUREDISPLAY_STATUS__SUCCESS) {
> +				int pos = 0;
>  				memset(i2c_output,  0, sizeof(i2c_output));
>  				for (i = 0; i < TA_SECUREDISPLAY_I2C_BUFFER_SIZE; i++)
> -					sprintf(i2c_output, "%s 0x%X", i2c_output,
> +					pos += sprintf(i2c_output + pos, " 0x%X",
>  						securedisplay_cmd->securedisplay_out_message.send_roi_crc.i2c_buf[i]);
>  				dev_info(adev->dev, "SECUREDISPLAY: I2C buffer out put is :%s\n", i2c_output);

Perhaps use a hex output like:

---
 drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c
index 9cf856c94f94..25bb34c72d20 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c
@@ -97,13 +97,12 @@ static ssize_t amdgpu_securedisplay_debugfs_write(struct file *f, const char __u
 	uint32_t op;
 	int i;
 	char str[64];
-	char i2c_output[256];
 	int ret;
 
 	if (*pos || size > sizeof(str) - 1)
 		return -EINVAL;
 
-	memset(str,  0, sizeof(str));
+	memset(str, 0, sizeof(str));
 	ret = copy_from_user(str, buf, size);
 	if (ret)
 		return -EFAULT;
@@ -139,11 +138,9 @@ static ssize_t amdgpu_securedisplay_debugfs_write(struct file *f, const char __u
 		ret = psp_securedisplay_invoke(psp, TA_SECUREDISPLAY_COMMAND__SEND_ROI_CRC);
 		if (!ret) {
 			if (securedisplay_cmd->status == TA_SECUREDISPLAY_STATUS__SUCCESS) {
-				memset(i2c_output,  0, sizeof(i2c_output));
-				for (i = 0; i < TA_SECUREDISPLAY_I2C_BUFFER_SIZE; i++)
-					sprintf(i2c_output, "%s 0x%X", i2c_output,
-						securedisplay_cmd->securedisplay_out_message.send_roi_crc.i2c_buf[i]);
-				dev_info(adev->dev, "SECUREDISPLAY: I2C buffer out put is :%s\n", i2c_output);
+				dev_info(adev->dev, "SECUREDISPLAY: I2C buffer output is: %*ph\n",
+					 (int)TA_SECUREDISPLAY_I2C_BUFFER_SIZE,
+					 securedisplay_cmd->securedisplay_out_message.send_roi_crc.i2c_buf);
 			} else {
 				psp_securedisplay_parse_resp_status(psp, securedisplay_cmd->status);
 			}